π 0 and η meson production in pp collisions at 0.9, 2.76 and 7 TeV measured with ALICE LHC on the march November 2011 Boris Polishchuk (IHEP, Protvino), for the ALICE Collaboration

Why neutral mesons spectra in pp? Test perturbative QCD at highest energies ever reached important constraint for g → pi0, eta fragmentation functions  gluon fragmentation not well constrained from e+e- data  gluon fragmentation is more inportant at higher energies MC tuning Test phenomenological rules observed at lower energies (e.g., m T scaling, p T scaling) in a new energy regime Extraction of direct photon spectrum Reference to study nuclear effects in Pb+Pb

Neutral Mesons measurements: Photon Spectrometer (PHOS) PbWO 4 calorimeter crystals in 3 modules: R M =20 mm X 0 =8.9 mm ρ=8.28 g/cm 3 n=2.16 size = 22x22x180 mm Installed at a distance of 4.6m from IP Acceptance: |η|<0.13,Δφ=60 o PHOS

Neutral Mesons measurements: Photon Conversion + Tracking γ 's between beam pipe and the middle of TPC can be detected via conversion electrons in the tracking system p T (e+-) min = 50 MeV/c |η|<0.9, full φ coverage Probability of conversion ~8% Reconstruction efficiency ~67% TPC

Invariant π 0 cross section: Conversion, PHOS Completely different techniques with different systematics: excellent cross check! Conversion method provides very good inv. mass resolution at very low pT Calorimeter provides wide pT coverage

Invariant π 0 cross section: Combined result (conversion+PHOS) Good agreement between two techniques Tsallis function provides a good descriptions at all energies Tsallis function:

Invariant η cross section: Conversion, PHOS η at √s =7 TeV measured up to 7 GeV with conversion method and up to 12 GeV/c with PHOS No approved PHOS measurements at 0.9 and 2.76 TeV (lack of statistics, limited PHOS acceptance for η)

Invariant η cross section at √s = 7TeV: Combined result (conversion+PHOS) Good agreement between conversion method and PHOS Tsalis function provides goog parametrization

π 0 vs. NLO pQCD NLO pQCD (W. Vogelsang) PDF: CTEQ6M5, FF:DSS, scales:0.5 pT,pT,2pT While pQCD calculations at √s=0.9 TeV describe data well, they fail to desribe data at √s=7 TeV for all possible choises of FF pQCD predictions demonstrates different behaviour at high pT then data

η vs. NLO pQCD Agreement with pQCD for 0.9 TeV 7 TeV data overestimated

π 0 /η ratio Comparison with world data η/π 0 ratio at √s=7 TeV agrees with NLO pQCD η/π 0 ratio measured in ALICE Is consistent with the previous measurements

Conclusions NLO pQCD calculations cannot provide a consistent description of measured data at both beam energies: √s=0.9 TeV and √s=7 TeV State-of-the-art calculations describe the data at 0.9 TeV, however the calculations do not describe the measured cross section at 7 TeV, where the calculations overestimate the cross section and exhibit a different slope compared to data.